Self-reactivity during an autoimmune disease like insulin dependent diabetes mellitus can be controlled by central thymic and peripheral post-thymic mechanisms. Peripheral tolerance will be approached in this subproject in the context of pancreatic beta cells. Several investigators have found that beta cell antigens can either be ignored or they can induce tolerance via bone marrow derived APCs located in pancreatic lymph nodes. We find that innate or immature DCs in lymphoid tissues selectively process certain cell-associated antigens and induce peripheral tolerance in the corresponding CD4+ and CD8+ T cells. Our goal is to learn to deliver antigens efficiently to immature or innate DCs in situ for the purposes of peripheral tolerance. Thus, together with Dr. Tarakhovsky, we will first work out methods to control DC maturation in vivo, since this maturation is likely to be a critical step for converting DC function from tolerance (immature or innate DCs) to autoimmunity (mature or adaptive DCs). Secondly, we can then pursue data whereby spleen cells, pulsed with a defined protein, are selectively captured by DCs in vivo. This is followed by presentation of peptides to major histocompatibility complex (MHC) class I and II restricted, T cell receptor (TCR) transgenic T cells, which proliferate extensively. In the steady state, the T cells become tolerant to subsequent antigenic challenge, while in the presence of a maturation stimulus, immunity develops. After laying the groundwork with this ongoing spleen cell model, we will consider the processing of pancreatic beta cell lines by innate DCs. Finally, we will use specific endocytosis receptors to enhance antigen presentation by innate DCs in vivo, as an experimental and potentially therapeutic approach for dampening beta cell autoreactivity. With Drs. Nussenzweig and Ravetch, we will target antigens through two receptors known to mediate presentation on MHC class I and II products of DCs. The receptors are the decalectin DEC-205, and FcgammaRs for immune complexes. Together these Specific Aims will help develop a new proposed role for DCs in the innate or steady state in situ, which is to capture select cell-associated and soluble antigens and induce peripheral tolerance.